Over the lifetime of a well there are many instances when it may be desirable to temporarily seal certain pathways in order to open others. One of those instances may be during a frac operation such as in plug and perf.
In a plug and perf operation, the operator begins by assembling a perforating tool on the surface. The perforating tool typically incorporates a plug on the lower end. The plug, once moved into position and set, will lock into the casing walls and form a fluid tight seal preventing fluid from moving past the plug. Just above the plug is a setting tool. The setting tool, once actuated, moves the plug from an unset position where the plug can be run into the well to a set position where, as previously mentioned, the plug locks into the casing and blocks fluid flow. Just above the setting tool is the perforating gun. The perforating gun usually but not always consists of one or more shaped charges that, upon detonation, will form holes in the casing wall. Any type of perforating gun may be used, including other perforating tools such as jetting tools, etc.
Once assembled on the surface the perforating tool and plug are run into the well to the desired depth. At the desired depth the setting tool is actuated to move the plug from its unset position to its set position locking the plug into place. The setting tool then disconnects from the plug. After disconnection the setting tool and the perforating gun are raised to some point above the now set plug, preferably to a location adjacent to a hydrocarbon formation. Once the perforating gun is in place the perforating gun is actuated thereby forming holes or perforations through the casing wall. The perforating gun and setting tool are then usually but not always removed from the wellbore.
With the perforating gun and setting tools removed from the wellbore the well may be fractured through the perforations formed by the perforating gun. Fracturing usually occurs by pumping high-pressure fluid through the casing to the plug. The plug prevents the fluid from further downward flow as the plug forms a fluid tight seal and is locked to the casing. High-pressure fluid then flows laterally outward through the holes in the casing.
It is generally understood that the high-pressure fluid will follow the path of least resistance. Meaning in practice that the high-pressure fluid once it begins a fracture through one or more of the perforations the rest of the fluid tends to follow through that initial fracture and fails to create other fractures in the formation. Therefore, it is generally desirable, at some point, to temporarily seal off the initial flow path so that the high-pressure fluid may form additional fractures within the formation thereby rendering a more complete frac job which gives better access to the hydrocarbons within the hydrocarbon bearing formation.
In another instance it may be desirable to at least temporarily block all of the initial perforations and other leak points within the wellbore. Such a situation may arise when after the well has been produced for some period of time the hydrocarbon production begins to taper off to a point where it is no longer economically feasible to produce the well. In such an instance new fractures within the well are needed to access different portions of the hydrocarbons locked within the shale and hydrocarbon bearing formation. In such an instance, before new fractures can be produced within the well any points of fluid loss within the casing or within the formation are sealed off. If the various points of fluid loss are not sealed off the high-pressure fluid will merely proceed through the older fractures i.e. the path of least resistance. Temporarily blocking the fractures is desirable because it is rare for the older fractures to cease producing completely therefore after the well has been re-fraced operators usually prefer that the older fissures within the hydrocarbon bearing formation be reopened to continue producing so that every last drop can be removed from the well. Once the well has been treated to block off fluid leak points within the casing such as previous perforations etc. the well may be again fractured using a plug and pert or other operation.
In still other instances it may be desirable to block off the more permeable sections of the wellbore in order to treat other less permeable sections of the wellbore. For example, the flow path through one portion of a wellbore may become obstructed due to paraffin build up, asphalt build up or other issues within the wellbore. In such a case the more permeable sections of the wellbore are temporarily blocked off in order to force a treatment regime into the less permeable sections of the wellbore in order to restore circulation. Once the treatment is complete it is desirable for the more permeable section of the wellbore to be reopened to produce fluids in addition to the previously less permeable section of the wellbore.